The invention relates to a method for controlling a valve for an exhaust system of a vehicle, and in particular a valve used for controlling the flow of exhaust gas through a heat exchanger.
A heat exchanger is part of auxiliary heating systems, which are increasingly used in vehicles having modern combustion engines with low fuel consumption. These combustion high efficiency engines produce, only a small amount of lost heat that is available for the heating system for the vehicle. This results in a reduced heating performance of the heating system, which may be uncomfortable to a vehicle's occupants. Accordingly, auxiliary heating systems have been developed that use a heat exchanger located in the exhaust system of the vehicle. The heat exchanger allows a gain of a certain portion of the heat of the exhaust gas, which is then available for heating the interior of the vehicle.
Auxiliary heating systems typically have an exhaust gas duct, in which the heat exchanger is located, and a bypass duct. By controlling a portion of the overall exhaust gas flowing through the heat exchanger duct, a desired heating characteristic of the auxiliary heating system can be obtained. To this end, a valve is provided, which is controlled depending on external parameters.
In general, a heat exchanger offers additional resistance to the exhaust gas flowing through the exhaust system, leading to a pressure drop. This pressure drop adds to the back pressure of the exhaust system, which in general is to be kept low to achieve good engine performance. Under some conditions, and in particular in cold weather conditions, the aim of providing better heating performance by directing the exhaust gas through the heat exchanger may result in a conflict with the aim of providing good engine performance by keeping the back pressure of the exhaust system low.
Therefore, there is a need for a method for controlling a valve in an exhaust system such that good heating performance is achieved, while at the same time ensuring that the pressure drop across the heat exchanger, and, accordingly, the back pressure of the exhaust system does not exceed given limits.